I don't know what else you would refer them as since they're immigrants that immigrated illegally. It's not a particularly easy and short word and it could be dehumanizing if you refer to somebody specifically as an illegal immigrant, but that usually isn't the case. Most people refer to the term when talking about illegal immigration and trying to come up with fancy politically-charged terms for something rather than it's actual legal term is really roundabout (aka stupid)
If you have a problem with the term then that's pretty much your problem, not everyone else's.